I bought it yesterday after trying out a bit. Then I used it for more than 1 hr in WvW to really experiment w/ it. My opinion is the tool is very useful to detect blobs running behind walls/obstacle so you can spot them immediately for defending's tower/keep. Other than that, in open fields, you will see them w/o the tool anyway. There isn't anything in there really useful, that we can do w/o, besides what I have just mentioned above. If you can implement the FoV, then it will definitely warrants its price. And you might increase the price a bit for 2 useful features, if elected, like $15. My opinion of course.

Suggestion: if your server is dead, it's nice to exit graciously instead of crashing & close GW2 to cause GW2 to create a report w/ all fatal errors. You just tell Anet that somebody was using your program.